Vehicle internal combustion engines typically comprise a front end belt driven accessory drive. The accessories can include power steering, an alternator, water pump and so on. The accessory drive can also be referred to as a serpentine drive since the belt often traces a circuitous path about the front plane of an engine.
A typical serpentine drive system includes a driving pulley on the crankshaft of an internal combustion engine of the vehicle, a series of driven pulleys for the accessories and a poly-V belt trained about the driving and driven pulleys. An advantage of the serpentine drive is that by providing an automatic belt tensioner on the belt the accessories can be fixedly mounted.
Particularly where the engine is of the four-cylinder type, the driving pulley establishes a highly dynamic loading on the belt. This high dynamic loading is due to the variable torque output characteristics of the crankshaft. A belt tensioner cannot accommodate all of the variable torque characteristics. The result can be noise and decreased belt life due to instantaneous belt slippage.
Representative of the art is U.S. Pat. No. 5,139,463 which discloses a serpentine belt drive system for an automotive vehicle in which the sequence of driven assemblies includes an alternator assembly comprising a housing and an armature assembly mounted in the housing for rotation about an armature axis. A hub structure is carried by the armature assembly outwardly of the housing for rotation therewith about the armature axis. A coil spring is disposed in operative relation between the alternator pulley and the hub structure for transmitting the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the armature assembly is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient rotational movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof.
What is needed is an isolator having a torsion spring exerting an axial contractive force to retain the pulley on the shaft. The present invention meets this need.